The invention relates to automatic positioning of a web of fibers on a mold for the production of various parts such as aircraft wings, means of a composite strip consisting of fiber elements which are sized (for example by impregnation with epoxy resin), pre-cut to the desired shape and dimensions, and maintained between two protective pellicles until they reach the location at which they are applied on the mold. As a rule, the top pellicle consists of a paper strip having suitable mechanical and chemical characteristics whilst the bottom pellicle consists of a very thin plastic film. The composite strip thus formed, the width of which is often within the range of 25 to 150 mm and the length of which is approximately 250 m, is provided in the form of a coil carried by an orientable part known as a "lay-up head".
The technique consists in depositing on the mold, with the highest possible degree of accuracy, the fiber elements (already cut-out and impregnated) which are conveyed in the form of the composite strip aforesaid. To this end, machines of current types are equipped with a device such as a roller or a shoe for applying the strip of fibers on the mold, the top strip of paper being recovered after it has passed beneath the application roller, the bottom protective film having been withdrawn prior to application of the fibers against the mold.
The lay-up head which supports in particular the coil of composite strip, the reels for recovery of the protective pellicles and the application device is carried by a structure which is similar to a gantry, for example, and serves to displace the lay-up head in translational motion along a longitudinal axis X (or feed-motion axis), a transverse axis Y and a vertical axis Z, as well as in rotation about the axis Z and about a horizontal axis oriented in the direction of feed motion of the machine.
The lay-up head and therefore the strip-applying device can thus be positioned and oriented, usually under the control of a numerical control unit, in order to deposit the composite strip in accordance with the profile which has been chosen.
Machines with the aforementioned lay-up head which is capable of moving along five axes are known and have been described for example in U.S. Pat. No. 3,775,219 and French patent 2,529,871.
In order to obtain good quality of stratification, it is necessary to ensure that the deposited composite strip is applied by the application device as symmetrically as possible over the entire width of the strip. For this reason, in French patent No. 2,529,871, it is proposed that the axis of rotation of the lay-up head, which is horizontal, passes through the mid-point of the line of contact of the strip with the surface to be covered.
However, this device is still subject to certain disadvantages which prevent the achievement of the desirable quality for certain applications, in particular the aircraft industry.
In fact, if the surface to be covered has been modified by the webs which have already been deposited or if said surface has not been defined with sufficient fineness, the numerical control unit is not capable of adapting the orientation of the application device to these specific conditions. In patent No. FR 2,529,871 cited earlier, steps have been taken to ensure that the means for controlling the oscillations of the lay-up head along the axis parallel to the X-axis are made dependent on detectors for sensing the proximity of the surface to be covered. However, in this case, the orientation of the entire lay-up head has to be modified. Together with all the accessories which it carries (reels, application roller, circular sector, etc.), this represents a substantial weight and inertia, thus resulting in response times which are detrimental to the quality of stratification or which make it necessary to reduce the lay-up speed.
U.S. Pat. No. 4,591,402, the teachings of which are included here by way of reference, has proposed to mount the application roller by means of an articulation. However, whether this articulation is constituted by pivot-pins or roller tracks, it appears that the position of the roller cannot be controlled with a sufficient degree of accuracy.
The present invention has for its object to overcome this disadvantage by incorporating an articulation along a horizontal axis on the support of the strip application member so that the orientation of said member is instantaneously adapted to the variations in profile which are encountered without being attended by the disadvantages of known articulations.